1. Field of the Invention
The present invention relates to a flatbed scanning type image reading apparatus for reading an image of an original by planar combination of main scanning and sub-scanning of the original and, more particularly, to an improvement for high-resolution wide-range image reading.
2. Description of the Background Art
There have been methods of optically reading images at high resolution by using a scanner having a wide reading area.
One of the conventional methods is such that a scanner comprising an optical zoom system and a lens switchable optical system limits an area to be read to read only a readable area of an original which is consistent with a high resolution.
Another conventional method is shown in the conceptual plan view of FIG. 14. A high-resolution lens system 901 is provided, and a plurality of linear photodetectors 902a to 902c are arranged at the imaging position of the lens system 901 in a line or substantially in a line in a main scanning direction. The photodetectors 902a to 902c detect respective partial images at high resolution. The image signals provided from the photodetectors are synthesized to form full image signals.
The above described conventional methods have drawbacks to be described below.
The first conventional method wherein the optically readable area is small has failed to read the full area of a large-sized original at high resolution. Further, this method has required a restriction in the position where an original is placed in many cases.
The second conventional method has involved the plurality of photodetector arrays to increase the size of the optical system and fabrication costs.